Author: Jonas Bilinkevicius 

In a TOpenDialog, you can set the initial directory. How do I set it as the 
desktop? I could set it as c:\windows\desktop, but then what if Windows is not on 
the user's c drive?

Answer:

There is a shell function that can be used to inquire about the location of several 
shell-related folders. You need to add ShlObj to the uses clause for this, plus 
ActiveX for the CoTaskMemFree.
1   
2   procedure FreePidl(pidl: PItemIDList);
3   begin
4     CoTaskMemFree(pidl);
5   end;
6   
7   procedure TForm1.Button2Click(Sender: TObject);
8   var
9     pidl: PItemIDList;
10    buf: array[0..MAX_PATH] of Char;
11  begin
12    if Succeeded(ShGetSpecialFolderLocation(Handle, CSIDL_DESKTOP, pidl)) then
13    begin
14      if ShGetPathfromIDList(pidl, buf) then
15        ShowMessage(buf);
16      FreePIDL(pidl);
17    end;
18  end;


See win32.hlp (or better msdn.microsoft.com, the list has been extended for Win98/2000) for a list of CSIDL values. There is also a newer ShGetSpecialFolderPath API that directly returns the path, but it is not available on older Win95 and NT installations.